Peter J. Frosch, Johannes Geier, Wolfgang Uter, An Goossens
Commercially available patch test kits (standard series and various supplementary series) are the basis of a diagnostic work-up if an allergic contact dermatitis is to be confirmed. However, various investigators have shown that this way of testing is not sufficient. Menné et al.  found in a multicenter study that the European Standard Series detects only 37-73% of the responsible allergens in patients with contact dermatitis. The additional and/or separately tested allergens were positive in 5-23%; the authors emphasize the necessity of testing with the products actually used by the patient. In Italy, an analysis of 230 patients referred to a contact clinic because of suspected occupational contact dermatitis showed that the standard series alone detected 69.9% of all cases considered to be of an allergic nature ; 26.3% of all allergic cases were positive only to supplementary series. The agents most commonly responsible for allergic contact dermatitis were metals and para-phenyl-enediamine.
In a German study of the IVDK network, the data of 2,460 patients tested between 1989 and 1992 were evaluated . In 208 patients (8.5%) type IV sensitizations were found to a total of 289 materials. In 44% of these cases only the patients' own products were patch test positive and thought to be clinically relevant.
In a subsequent analysis of 1998-2002 data, 8.6% of 3,621 patients had a positive patch test reaction to their own skin-care products additionally patch tested. Of 1,333 patients, 5.3% were tested positive to their own bath and shower products. In about one-third of the patients reacting to either product category, further positive tests to commercial allergens were not observed [1,29].
The materials most frequently tested are usually topical medications, cosmetics of various types, rubber and leather products.
The group of Kanerva has published an impressive series of papers in which patch testing with the patients' own industrial chemicals has provided the main clue as to the causative agent of allergic contact dermatitis . Various constituents of plastic materials, epoxy glues and paints, reactive dyes, and industrial enzymes were identified after chemical analysis. With regard to isocyanates present in polyurethane resins, for example, it was found that among 22 occupationally related cases, 21 reacted to the isocyanates obtained from the companies involved (13 x) or to diaminodiphe-nylmethane (marker for isocyanate allergy), but only 1 reacted to the commercially available isocyanate, diphenylmethane diisocya-nate or MDI (Trolab, Chemotechnique) . Indeed, Frick et al. , when analyzing 14 commercial preparations of MDI, found that in most cases its concentration did not match the one stated on the label. Moreover, the isocyanates tested are not always representative of the mixtures used in industry.
Recently, reports were published on contact allergy to the patients' perfume where the current fragrance mix and the commercially available major allergens of perfume remained negative. After repeated testing with various fractions of perfumes the causative allergens were identified: Lilial  and coumarin . The experience with perfumes has shown that in this dynamic field, with rapid changes in trendy attractive smells, the consumer is exposed to a wide array of chemicals that may cause sensitization. This subject is reviewed in detail in Chap.31, Sect. 31.1. Further examples documenting the high value of testing with the patients' own products are published elsewhere [17-19,28]. In this field and in many industrial areas,patch testing with merely the standard and supplementary series will always be inadequate until new allergens have been identified, their clinical relevance has been confirmed by several study groups, and they are eventually included in a test series.
In the following we want to give guidelines for testing with patients' own materials in order to harmonize this approach in daily practice. Knowledge in this field is often minimal and profound mistakes are made. For example, concentrated biocides or plastic monomers are applied under occlusion in undiluted form causing bullous or ulcerative lesions and possibly active sensitization. In contrast, the material is not infrequently diluted too much or in an inappropriate vehicle resulting in a false-negative reaction.
The guidelines are presented mainly in tables in order to be used at the work bench by technicians. They contain essential information; for more detailed information the reader is referred to other chapters in this book (particularly Chap. 49) and the pertinent references listed at the end.
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